Antispin attachment for link trainers



- septf 5, 1944.

M. c. BALSAMO ANTISPIN ATTACHMENT FOR LINK TRAINERS Filed Aug. 5, 1943 2Sheets-Sheet vl N .mi

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Sept. 5, 1944. l vVM. c.v BALSAMC? ANTISPIN ATTAGHMENTAEEINK TRAINERS YFiled Aug. 5, 1945 1N VEN TOR M/CH/qeL C. 544

A TTORNE YS Patented Sept. 5, 1944 om'rso STATES Param* ortica ANTISPINATTACHMENT FOR LINK TRAINERSV Michael C. Balsamo, Dayton, OhioApplication August 5, 1943,y serial No. 497,537 6 claims. (C1. :i5- 12)(Granted under the act of March s, 1883,v as amende'dApril 30, 1928; 370O. G. 757) kof vacuum to the stall valve bellows is necessaryfor normaloperation; consequently the trainer begins to spin immediately uponturning on the turbine which provides a vacuum source for all thediiierent bellows and vacuum lines of the trainer. Heretofore, it hasbeen necessary for the instructor prior to turning o-n the turbine toremove a side panel from the ktrainer fuselage and reach in and takehold of the inverted pendulum, which is a part of the stall valveassembly, so that the student could climb into the trainer and be seatedand'assume full control without being subjected to the spin. The generalobject of the invention is to provide a mechanism which willautomatically prevent the trainer from spinning when the turbine is rstturned on, while permitting all parts of the trainer to functionnormally at all other times. The invention thus saves the time of theinstructor and also that of the student, since the latter need no longerdirect his attention to recovering fromV a spin before proceeding withthe assigned problem. The preferred mechanism is a very simpletime-delay device which prevents the stall valve pendulum from moving toitsY operative position for a predetermined time after the trainer isstarted. Further objects are to provide a device for the purpose statedwhose cost is negligible and which is easily installed and requireslittle or no maintenance.

Reference should be made to Link Patent No. 2,099,857, dated November23, 1937, for a fuller understanding of the Link trainer.

In the accompanying drawings,

Fig. l is a perspective view of the stall valve assembly of a Linktrainer with a stop device attached thereto, in accordance with theinvention;

Fig. 2 is a sectional elevation of the stop device per Se;

Fig. 3 is a detail view in elevation; Fig. 4' is a perspective view ofthe mechanism for causing the trainer to spin, together with therudder-controllingv pedals, certain associated parts; and

Fig. 5 is a perspective of the spin valve assembly, which deter-minesthe direction of spin.

Fig. 6 is a side elevation of a Link trainer fuselage, minus the wing,showing the location of the stall valve assembly of Fig. l.

Referring particularly to the drawings, the stall valve assembly of Fig.l (corresponding in function to the stall valve of Figs. 14, 22 and 23of said Link patent) comprises a stall valve bellows I0, one end ofwhich is secured to and carried by a bracket II which may be anextension of one arm of a V-shaped upright frame I2. Integral withV-frame I2- and extending at right angles is a horizontal base plate I3which may be screwed to the floor of the trainer cockpit (not shown).The stall valve body I4 is fixed on base plate i3 and has a vacuum lineI5 to the trainers climb-k dive Ytank (not shown) controlled through aneedle valve (hidden by valve body I4) and also has-an atmospheric inletI6 and an air lter I1 at the upper end of the inlet I6. A valve stem I8projects from one end of the valve body to a point between the arms ofthe V-frame, and an'inverted pendulum I9 is secured at its lower end tosaid valve stem to turnthe same o-n its longitudinal axis thereby toopen and close theneedle valve by means of a left-handed screwv threadnot shown. The inverted pendulum I9 oscillates in a vertical arc and hasa weight. |l at-its upper vend and a longitudinal slot |91) forreceiving a stud 2l which is tightened at any point along the -slot by anut, 22. Stud 2| transmits movement of the inverted pendulum to orreceives movement from a slotted bar 23 (slidably mounted on the upperends of the two armsof the V-irame) by contact Witheither of twovertical ngers 24, 25, adjustable along the respective slots of bar 23.Clamping screws 26 secure iinger's 24, 25, at the desired points. A stopscrew 21 is screwed through one of the arms of the V-frame near itsupper end and is so 1ocated that one end may be engaged by the invertedpendulum to limit its arc of movement in one direction.

When the speed of an airplane drops below a certain minimum, theairplane stalls and sometimes starts to spin. This characteristic isbuilt into the Link trainer. The bellows I0 is connected by tubing 28 tothe vacuum line extending from the -air speed regulating bellows to theair' speed transmitter (not shown), so that the same Vacuum is appliedto the stall valve bellows as to the air speed transmitter. At normalair `42, 44, i-s always under speed, this suction is strong enough tokeep the bellows i6 collapsed, overcoming the'tension of spring 29. Oneend of spring 29 is anchored to the rear wall of the cockpit or otherconvenient upright fixed member 29a, while the other end is secured tobellows I!) (Fig. 3) in such a manner as to oppose the collapsing of thebellows by vacu-um suction. In this position, the bar 23, one end ofwhich is pivotally attached to the movable part of the bello-ws, holdsthe inverted pendulum (by engagement of finger 25 with stud 2|) in itsforward position against the stop screw 21. The atmosphere is thenentering atmospheric vent 30 in a three-way jet assembly 3| and betweenthe line from the main vacuum supply and the line 32 to the spin-tripbellows 43 (to be described). See Fig. 4. A corresponding atmosphericvent is v not found in said Link patent. Due to a restriction built into the vacuum side of this connection, the atmosphere entering vent 30is sufficient to reduce the vacuum to the spin-trip bellows line 32 sothat the spin-trip bellows remains open; As the simulated air speed isdecreased, the suction on the stall bellows is correspondingly reduced,and when the suction is suihciently reduced, the tension of spring 2Boverpowers the suction. and opens the stall bellows. As the stallbellows opens, bar 23 by means of iinger 24 pulls the pendulum backtoward the other arm of the V-frame. This opens the stall valve andcloses vent 30 (by a seal 33 on the pendulum, to which there is nocorresponding part in said Link patent) to permit full suction to beapplied to the spin-trip bellows causing the trainer to spin.

Before describing the attachment, the action of the mechanism foreffecting automatic spin of the trainer should lbe made clear. Referringto Fig. 4, the bank-turn shaft 4U is solid and supports a hollow shaft4|, which is sometimes free to turn and, at other times, is locked tothe bankturn shaft. Three bellows 42, 43, 44, are mounted on the hollowshaft 4|, together with a latch 45; the spinbellows 42 and 44 at the topand bottom actuating the rudder valve in opposite directions when thetrainer is spinning and intermediate bellows 43 (the spin-trip bellows)working the latch 45, as will be described. Compare Fig. l2 of the Linkpatent, which shows a somewhat similar arrangement. One of the spinbellows vacuum, hence collapsed, while the other is expanded under theaction of a V-shaped spring 46, there being one of said springs for eachof the three bellows. An arm 41 is secured at one end to the solid innershaft 46, and has a notch 41a for receiving latch 45. Another arm 48,which carries the latch, is anchored at its opposite end to the hollowshaft 4|. Latch 45i-sv pivoted as at 45a upon an arm 45b fixed to thespin-trip bellows, and as long as it engages arm 41, the two shafts 40,4|, are locked together and the assembly functions only to provide anautomatic turn with banking. When the simulated air speed falls belowthe predetermined stalling speed, the pendul-um I9 closes vent 30,causing increased vacuum line 32 to the spin-trip bellows 43. Thisincreased vacuum closes this bellows which moves latch 45 out of notch41a in arm 41. The hollow shaft 4| is still held rigid by an arm f49(which is connected to banking rod 50 extendingA down through the floorof the fuselage to the trainer octagon 85), but arm 41 and the innershaft 46 are free to turn. Assuming that vacuum is being applied to thetop bellows 42, with the to be applied to the.

latch released, as described, the top bellOWs Closes, 75

pushing arm 41 down by means of rod 5|, link 52 and pin 53, and rotatingthe inner shaft 46. This swings a bell crank 54, which moves walkingbeam 55, pulling the rudder valve 56 wide open by means of a rod 51,causing the trainer to spin. Figs. 8, 9 and 12 of said Link patent showa corresponding rudder Valve. The rudder valve is connected through atube S6 with the motordriven vacuum turbine (not shown) which is thesource of vacuum for all vacuum-operated parts of the trainer. Tubes 9|,92 connect the rudder valve with the turning motor (not shown).

Selection of the particular spin bellows 42, 44 which shall be undervacuum is the function of the spin valve 60 (Fig. 5). Compare Figs. 12,24 and 25 ofthe Link patent, parts 236 to 244 inclusive. This valve is atwo-way valve connected on one side to the vacuum supply through line aand on the other to both spin bellows through lines 60h, 60C. It has aninverted pendulum 6|, whose position determines the bellows to whichvacuum shall be applied. Pendulum 6| normally falls toward the lowerside of the fuselage but can be thrown to the opposite side by use ofpivotally mounted rudder pedals 62, 63, through a fork 64, which extendsback from the rudder bar 65. Rudder bar 65 is swung by foot pressure onthe rudder pedals, which is transmitted through wire cables 65a, 65h tothe ends of the rudder bar. Pedals 62, 63 are normally balanced or heldin upright position by tension coil springs 62a, 63a, respectively,which keep the cables 65a, 65D under tension. Said coil springs areanchored at their opposite ends to the cockpit footboard 62h or otherstationary part of the fuselage. Rudder bar 65 has rods 65e attached toeach end thereof (only one, however, being shown in Fig. 4) andconnected to the rudder 83 (Fig, 6) of the trainer soas to turn therudder when the pedals 62, 63 are depressed. Stops 66, 61 for pendulum6| are provided by the ends of a stationary frame 68, which mounts thespin valve 66. As long as the air speed remains below stalling speed,spintrip bellows 43 will remain collapsed and the latch 45 will remainraised where it cannot engage notch 41a in arm 41. During this time,full application of the opposite rudder will throw the spin Valvependulum 6| over and apply vacuum to the other spin bellows. As thisbellows collapses, it will swing arm 41 past latch 45 and will move therudder valve around to fully open position inthe opposite direction.This will reverse the direction of the spin, but normal rudder controlcannot be regained until normal air speed is attained. To recover from aspin in the Link trainer, it is necessary to nose down to regain normalair speed, and also to apply the rudder for a full turn in the directionopposite to that of the spin. When normal air speed is attained, thestall valve pendulum I9 moves away from vent 3|), allowing theatmosphere to enter, which decreases the vacuum to the spin-tripbellows, whereupon the latter expands responsive to its spring 4S. Thisreturns latch 45 to its locking position. The application of fullrudder, already mentioned, throws the spin valve pendulum 6| over,whereupon the other spin valve bellows starts to collapse, attempting toswing arm 41 past the latch. But the latch, now in normal position,engages notch 41a and thus locks shaft 40, restoring normal ruddercontrol.

Mounted on the stall inder valve bellows l!! is a cyl- 10 secured byscrews 1| passing through a bracket 12, Within the cylinder is a conicalcoml pression spring 'I3r (Fig.2), one end of which abuts the end wallof the cylinder, while thek other end presses against a piston 'Mhavinga rod 'I5 extending out-side the cylinder. The piston rod constitutes aretractible stop which Vis engaged by the pend-ulum I9, whenever thelatter moves toward the vent 30, provided the piston rod 'I5`is extendedbythe spring as illustrated in Fig. 1. Thus the seal 33 cannot close thevent 30, and the trainer will not spin, so long as the retractible stopis in the path of the pendulum. A vacuum line 'I6 from the manifold (notshown), which is connected with the vacuum side of the turbine, leads tothe upper end of the cylinder, but due to a bleed-hole I'I in thecylinder this vacuum is not immediately eiective in drawing the pistonup to the top of the cylinder against the compression of the spring.Bleed hole 'I'I lets atmospheric air in the cylinder, when suction isapplied thereto, and reduces the vacuum, hence increases the time delayof the device, which may be about six seconds. Another small hole 18, inthe lower end of the cylinder, facilitates movement of the piston towardthe bottom of the cylinder.

The operation is as follows:I When the turbine is rst turned on,pendulum I9 moves toward stop 21 before the retractible stop 'I5 isretracted within the cylinder. Thereafter, the stall valve a-ssemblywill function normally, and the trainer will start to spin if thestudent permits the indicated speed to fall below the stalling speed.This is as it should be. When the turbine is turned off, the conicalspring overcomes the reduced vacuum in the cylinder, pushing stop 'I5 toits extended position (Fig. 1) before pendulum I9 moves toward vent 30.Therefore, the pendulum can never seal said vent when the trainer is outof operation, and the undesired initial spin e already described cannever take place.

The usual location of the stall valve assembly, as indicated in Fig. 6,is below the removable seat on which the `student sits while in thecockpit. Access to the cockpit is through a door 80 hinged to a sidewall of the trainer fuselage 8l. A hood 82 may be lifted or lowered atwill, and when lowered will completely shut off the students Vision,-forcing him to fly on instruments. A rudder 83 and horizontalstabilizer 84 are also shown. The trainer Octagon 85, which revolveswith the fuselage, is indicated. The wing, which would normally appearbelow and to the left of door 80, has been omitted for clearness, and,of course, many details are omitted because of the small scale of thefigure,

Bracket 12, which secures the cylinder to the bellows I0, is adjustable(not shown), hence the device may be mounted on all the different modelsof Link trainers. As the attachment is very simple, its manufacturingcost is quite low, and installation and maintenance costs arenegligible. The described arrangement permits the altimeter of thetrainer quickly to attain its lowest reading when the turbine -is shutoff, which is a distinct advantage.

Obviously, other known forms of time-delay'devices may be used toperform the same function as the device described above. Furthermore, aswill be clear to those skilled in the art, it is unnecessary to mountthe attachment on the stall valve assembly, as there are other point-son the Link trainer where a time-delay device may be used to prevent theinitial spin mentioned above. Some of the parts of the Link trainershown in the drawings but not claimed herein may be covered by` claimsin pendingapplications owned by or'licensed to' Link AAviation Devices,Inc.

Having described my invention, what I claim as new'and desire to secureby Letters'Patent is:

1. For use in an aviation ground trainer of the character wherein avfuselage forming a cockpit enclosure is provided with student-operated'control means operativev to control power means for causing tilting orivrotational movement of the 4fuselage about a base and having a valvemeans for causing rotation -of the trainer fuselage to simulate anairplane spin condition upon decrease in indicated air speed to apredetermined value; that improvement which consists, in combinationwith said valve means, of a time delay means associated with said valvemeans and operative upon energizing of said trainer power means torender said valve means inoperative for a predetermined period of time.

2. In combination with the spin-trip bellows and the stall valveassembly of a Link trainer, said stall valve assembly having an invertedpendulum, a seal on the pendulum, a vacuum line leading to the spin-tripbellows to operate the same, said vacuum line having a vent to theatmosphere, and the seal being adapted to close said vent to render thevacuum line operative; a stop device having a part which automaticallymoves into the path of said inverted pendulum to prevent said pendulumfrom sealing said vent; said automatic movement taking place invariablywhen the turbine which actuates the trainer is out off; said stop devicebeing constructed and arranged so that it automatically moves out of thepath of the pendulum after a time delay when the turbine is started.

3. The invention according to claim 2, wherein said stop devicecomprises a cylinder, a springpressed piston in the cylinder, and apiston rod; the piston rod extending outside the cylinder, when thespring is effective, to act as a stop for the pendulum; and a vacuumline connected with source of vacuum of the trainer and also to thecylinder to draw the piston rod up in the cylinder against theresistance of the spring.

4. An attachment for the stall valve assembly of a Link trainercomprising, in combination, a bracket adapted to be mounted on the stallvalve bellows; a cylinder secured by said bracket; a piston reciprocablein said cylinder; a piston rod extending outside said cylinder andadapted to act as a stop for the inverted pendulum of said assembly whensuiciently extended; a vacuum line connected to the cylinder; a springin the cylinder acting against the piston in opposition to the suctionofthe vacuum line; and a bleed hole in the side of the cylinder toretard movement of the piston responsive to the vacuum suction.

5. in combination with the stall valve assembly of a Link trainer, atime delay device having a part which always tends to project into thepath of the inverted pendulum of that assembly as said pendulum movestoward the vent which leads to the spin-trip bellows; and means actuatedby .and upon turning on the trainer to cause said part to move out ofsaid path after a predetermined time delay, so that the stall valveassembly is restored to its normal operating condition.

6. For use in an aviation ground trainer of the in combination with saidspin-trip bellows, of mechanism attached lto the trainer toautomatically prevent the application of su'cient Vacuum to operate thespin-trip bellows when the trainer is rst turned on, said mechanism'having a time delay action to permit normal operation of the spin-tripbellows a short time after the trainer is turned on.

MICHAEL C. BALSAMO.

